Went to get some new plugs today for my EL XR8. Was going to get iridium platinum ones but the part number in the book does not match the plugs I need. I bought a set of plugs from ebay a while ago and they were also wrong. Mine I pulled out have a 20mm long thread and the ones I bought and ones they showed me at the shop had about a 10mm thread. At the moment I have Champion RS12YC6 plugs in it and they are really stuffed. Any one know of a cross referance chart?

Ngk have a cross referance tool on there web site.

http://www.ngk.com.au/CrossRef/crossref.php

the ones with the short thread will be the correct ones. the ones with the longer thread will be for gt40p heads. both will work though.

How do I tell if I have GT40p heads? It's an ex police model.

gt40p heads didn't come out as std equipment until the au's so its very unlikely you have them unless the car has been modified since leaving the factory.

if you look at no. 1 spark plug you should see the letters 'gtp' stamped in the head on an angle toward the front of the head. there are other distinguishing marks but not easy to see while bolted up. the spark plugs come out on much less of an angle than the e7's as well.

Would an AUII XR8 with the Tickford plate ( biulder signed) have the gtp heads????

every au, tickford or not got the gt40p heads.

the 220kw heads also got bigger valves. my knowledge is limited at best though so i can't give too many details.

i think the series 1 or 2 't' series got svo alloy heads instead.

I just tried to see but you need to be a master plumber to see what going on down there.

if you struggle to see it its probably not there. it is fairly easy to see on mine, just by no.1 plug behind the alternator.

chances are the plugs you originally pulled out were wrong fitment by whoever did the last service. it shouldn't make too much difference to the performance of them though. could make them harder to get in and out as the last 10mm of thread will get fouled up with carbon.

when i bought my car i had similar situation. i bought new plugs and when i pulled the ones that were in there out i found they were longer thread. i got all worried that i'd bought the wrong ones so jumped in my other car with both types of plugs and headed back down to teh shop and sussed it out with them. the ones i had in were for a sprint/gt/au.

std e7 heads, which is what you should have if they have not been changed, will take the plugs with about 10mm thread.

I checked the wrong side, dumb a** is me.